High-altitude adaptation in humans

Certain human populations around the world have the natural ability to survive and live comfortably at high altitudes as a result of evolutionary adaptation, which causes irreversible and long-term physiological responses to high-altitude environments associated with heritable behavioural and genetic changes. These populations are indigenous inhabitants of highly elevated regions on Earth, including Tibet and the Andes, and hence thrive in conditions that would cause the rest of the human population to suffer serious health consequences. The capability, or lack thereof, to sustain oneself at a high elevation without the aid of specialized devices (such as a breathing apparatus) is particularly due to structural and functional differences in the regulatory systems of oxygen respiration and blood circulation.

Around 81.6 million people (roughly 1.1% of the global population) live permanently at altitudes above 2,500 metres (8,200 ft) and as high as 5,100 metres (16,700 ft). Extended exposure to an environment higher than 2,500 metres (8,200 ft) above sea level normally induces chronic mountain sickness in humans, but many of the populations occupying permanent settlements at high altitudes throughout South America, South Asia, and East Africa have experienced these conditions for millennia without any apparent complications. This special adaptation is now recognized as an example of natural selection in action. The high-altitude adaptation of the Tibetan people is the fastest known example of human evolution, as it is estimated to have occurred in a span of less than 3,000 years at some point between 7000 BCE and 1000 BCE.